I have a struct I need to port from C but the size I’m getting in Pascal is wrong. From C sizeof(AAPLVertex) = 32 but in Pascal sizeof(AAPLVertex) = 24.

The alignment of the struct is on 32 bit bounds I think but how do I replicate this in Pascal so it behaves exactly like c? I tried using $align but it didn’t seem to have any effect.

{$align 32}
type
	TAAPLVertex = packed record
		position: vector_float2;
		color: vector_float4;
	end;
typedef struct
{
    vector_float2 position;
    vector_float4 color;
} AAPLVertex;

Regards,
Ryan Joseph

Hi,

The whole idea of a packed record is to ignore alignment and "pack" the fields ignoring padding and alignment. Use a normal record without "packed", or add the padding fields manually, if you still have to use a packed record for whatever reason.

BTW, $align specifies the alignment in *BYTES* not in bits. So to align to 32bits you need {$align 4}. But Free Pascal also supports {$packrecords C}, where it will try to mimic the C compiler's alignment as native to the target platform. In any unit which needs to interface to a C library, I'd use {$packrecords C} and no {$align}

This is all documented BTW at the respective directives...

Charlie

Ok, I see now. I tried adding {$packrecords C} in all units but the size still comes back as 24 instead of 32. So what is the C compiler really doing I wonder? I found out through trial and error I need 2 floats in-between both fields to get proper alignment but why is this? I hate to be adding random space into records which may break on other machines or if built with different compilers (I’m using ppcx64 btw if that matters).

type
	TAAPLVertex = record
		position: vector_float2;
		padding_0: simd_float;
		padding_1: simd_float;
		color: vector_float4;
	end;

Regards,
Ryan Joseph